Allow environment_variable directory to take a workload_group arg

This commit enables the workload_group argument within the
environment_variable application definition language directive.

lib/ramble/ramble/language/application_language.py

@@ -108,6 +108,10 @@ def _execute_workload_groups(app):
                 for var in app.workload_group_vars[name]:
                     app.workloads[workload].add_variable(var)
 
+            if name in app.workload_group_env_vars:
+                for env_var in app.workload_group_env_vars[name]:
+                    app.workloads[workload].add_environment_variable(env_var)
+
     return _execute_workload_groups
 
 
@@ -260,8 +264,10 @@ def _execute_workload_variable(app):
     return _execute_workload_variable
 
 
-@application_directive(dicts=())
-def environment_variable(name, value, description, workload=None, workloads=None, **kwargs):
+@application_directive("workload_group_env_vars")
+def environment_variable(
+    name, value, description, workload=None, workloads=None, workload_group=None, **kwargs
+):
     """Define an environment variable to be used in experiments
 
     Args:
@@ -274,15 +280,29 @@ def environment_variable(name, value, description, workload=None, workloads=None
     """
 
     def _execute_environment_variable(app):
-        all_workloads = ramble.language.language_helpers.require_definition(
+        all_workloads = ramble.language.language_helpers.merge_definitions(
             workload, workloads, app.workloads, "workload", "workloads", "environment_variable"
         )
 
+        workload_env_var = ramble.workload.WorkloadEnvironmentVariable(
+            name, value=value, description=description
+        )
+
         for wl_name in all_workloads:
-            app.workloads[wl_name].add_environment_variable(
-                ramble.workload.WorkloadEnvironmentVariable(
-                    name, value=value, description=description
-                )
-            )
+            app.workloads[wl_name].add_environment_variable(workload_env_var.copy())
+
+        if workload_group is not None:
+            workload_group_list = app.workload_groups[workload_group]
+
+            if workload_group not in app.workload_group_env_vars:
+                app.workload_group_env_vars[workload_group] = []
+
+            app.workload_group_vars[workload_group].append(workload_env_var.copy())
+
+            for wl_name in workload_group_list:
+                app.workloads[wl_name].add_environment_variable(workload_env_var.copy())
+
+        if not all_workloads and workload_group is None:
+            raise DirectiveError("A workload or workload group is required")
 
     return _execute_environment_variable